1. Field
The general utility of single mode optical fiber is perceived as being limited in long haul and other applications because of its limited information capacity. Multimode fibers have been introduced to increase transmission capacity but these multi-channel fibers, which transmit multiple optical modes in a single core or multiple distinct cores, are subject to channel crosstalk due to mode coupling effects. For example, mode coupling in multimode fibers can arise when an optical fiber or fiber bundle is subject to bending or twisting in its deployed state.
2. Technical Background
Digital signal processing techniques have been developed to deal with channel crosstalk arising from the aforementioned mode coupling. One type of this digital signal processing is commonly referred to as coherent multiple-input, multiple-output (MIMO) digital signal processing (DSP). MIMO DSP has been proposed and demonstrated widely but is limited to significant extent because it has proven difficult to deploy in systems of substantial transmission length, where the necessary error correction schemes become progressively more complicated with increasing transmission length.